1. Field of the Invention
This invention relates to a lens system, and more particularly relates to a wafer-level miniature image capture lens.
2. Description of the Related Art
Mobile phones or personal computers employing imaging devices have become popular due to employment of solid-state image capture elements such as a CCD (a charged coupled device) type image sensors, a CMOS (a complementary metal oxide semiconductor) type image sensors and the like, allowing for higher performance and miniaturization of imaging devices. Additionally, there is demand for further miniaturization of image capture lenses loaded on the imaging devices.
However, despite demands, limits for further miniaturization of image capture lenses are being reached, as for the conventional image capture lenses, because they are true three dimensional (3-D) structures and sensors therein need to also be miniaturized, it is difficult to control accuracy of lateral shift and tilt for each lens surface nor to handle tiny lens during fabrication. Namely, tolerance is less.
FIG. 1 shows an imaging device using a published wafer-level lens module system. Light passes through the wafer-level lens 102 and 104 to the sensing element 106. In this art, the wafer-level lens modules 102 and 104 and the sensing element 106 can be fabricated by VLSI process technologies. Therefore, the image device 100 can have a smaller size suitable for portable electronic devices, such as cell phones or personal digital assistants (PDAs). The wafer-level lens converts the true 3-Dimensional structure into a 2.5-Dimensional structure which stacks each lens plate into a lens cube. Thus, allowing for further miniaturization along with technological advances driven by semiconductor processes such as Moore's law, as tolerance is greater. Moreover, while conventional lenses are fabricated by a discrete process, which assembles the lenses one by one, in contrast, the wafer-level lens is fabricated by a batch process, which can stack thousands of lens on a lens plate into a lens module array, then singulate into a lens cube by die-saw process. However, despite the smaller volume, conventional 3-D lens currently outperform wafer-level lenses. Additionally, it is relatively more difficult to design a optical lens system with small enough aberration, good enough modulation transfer function (MTF), for wafer-level lenses, especially when Nyquist frequency is higher, than for conventional three dimensional (3-D) lenses. While MTF may be increased for wafer-level lenses by increasing the lens surface number, the lens total track would correspondingly increase in length.